1. Field of the Invention
The invention relates to an apparatus for treating the waste gases of metallurgic refining vessels wherein the waste gas is collected, cooled, cleaned and stored.
2. Description of the Prior Art
In the known refining methods, particularly the converter method, the waste gases leaving the refining vessel have a high temperature of 1450.degree. to 1600.degree. C. and contain significant amounts of dust, the concentration of which may reach an order of magnitude of 100 to 200 g/Nm.sup.3. From these two conditions, which can vary during the refining, significant problems develop in view of the large amounts of gases of approximately 2 Nm.sup.3 /min per ton of casehardening materials which are produced, although the amount of gases vary with time. These problems result primarily because a major portion of the waste gas is carbon monoxide which cannot be discharged into the atmosphere or flared for reasons of environmental protection.
The main features of the known refining methods with oxygen are the use of a converter for receiving the liquid crude iron and the solid admixtures, i.e., flux, scrap metals, etc., the converter being able to rotate about a horizontal axis, an arrangement for collecting and preparing the escaping reaction gases, as well as the batch-wise operation consisting of a sequence of individual method steps.
It is of special importance that the converter and the system for treating the waste gas are arranged at a certain spatial distance from each other. This results in the waste gas influencing the atmosphere by emission and/or the waste gas itself being influenced because of a reaction with the surrounding air. However, each of these effects are either completely undesirable or desirable only to a limited degree and, in some cases, must be completely avoided.
No matter what happens to the waste gas, a cleaning of the gas is always required in order to achieve dust contents in the order of magnitude of a tenth of a gram per normal or standard cubic meter. The costs of the cleaning of the waste gas are mainly determined by the temperature of the gas and by the volume of the gas. Therefore, the efforts in practice are directed to keeping the temperature of the waste gas as well as the volume of the waste gas as low as possible. Since the amount of waste gas and the temperature of the waste gas are mainly determined by the carbon content and the temperature of the melt, the prerequisite for an economical cleaning of the gas is to minimize the so-called "after-burning", i.e., the reaction of the carbon monoxide created during refining with the surrounding air. This aspect is of decisive importance since the after-burning leads to significant increases in the temperature and correspondingly, to proportionate increases, for example, a three-fold increase, of the volume of the waste gases.
The problem of sealing the system as extensively as possible became important because of the increasing size of converter units and the resulting increased amounts of waste gases. In open systems, these waste gases burn together with atmospheric air. As a result, the volume of the waste gases is multiplied and the temperatures are increased by several hundred degrees Celsius.
A known arrangement for closing the gap between the converter and the apparatus or arrangement for treating the gas, consists of a sleeve-like locking or sealing ring which can be raised or lowered. This ring makes it possible to have a certain control over the influence of the surrounding air. However, it is not possible to prevent the effects of the gas when an excess pressure buildup occurs during the process. The reason for this is that when there is excess pressure, any kind of leakage may lead to the emission of dangerous substances. In addition, a cumbersome drive and complicated, but ineffective, sealings are required for the locking or sealing ring. Furthermore, in order to raise the sealing ring into the open-position requires a building of sufficient height to provide a sufficient, free space, above the converter.
Methods are also known wherein the annular gap between the ring and converter aperture remaining after lowering the locking ring is sealed off by a veil or curtain of inert gas or water vapor applied under pressure. However, such a gas curtain can only be effective if the difference between the atmospheric pressure and the pressure of the waste gas is as small as possible. The amounts of waste gases vary considerably during refining and sometimes even tend to vary in a pulse-like manner. Therefore, a minimal difference in pressure or an insignificant excess pressure of the waste gas in the region of the gap can only be achieved with the aid of a quick response pressure control which balances the variations of the volume flow.
A pressure control having the required speed of response is extremely cumbersome and is not capable of completely suppressing the after-burning. For example, in the conventional apparatuses, there is usually about ten percent of after-burning. Accordingly, larger amounts of waste gases must be handled and an increased cooling capacity is required resulting in increased costs for the apparatus and for operation.
Another disadvantage of the use of more or less open systems lies in the fact that, due to the small amounts of carbon monoxide formed at the beginning and during the final stage of refining, an explosive mixture of carbon monoxide and oxygen may be easily formed if refining is interrupted or during operation at reduced pressure or when the openings are not carefully closed or locked. As a result, the converter and the components which convey the waste gas must be carefully washed out or rinsed. Finally, in the conventional apparatuses, there is also the great danger that the hood or dome or the locking ring will stick to the converter aperture due to metal and slag sprinkles or sprays.
Moreover, after-burning leads to a significant loss of energy since after-burning yields carbon dioxide which cannot be utilized and is only carried along as ballast gas and reduces the heating value of the waste gas. The heating value is essentially determined by the carbon monoxide content of the waste gas. Additional energy is required because of the weight of the charges and consequently, the amounts of waste gas produced per unit time have significantly increased. This, in turn, requires blowers with delivery volumes of several 100,000 m.sup.3 /h and delivery pressures of more than 200 mbar for transporting the waste gas through the treatment plant. Electro-motors with outputs of several MW are used for driving these blowers. These large units lead, among other things, to increased noise emissions which must be counteracted by additional measures.